This invention is concerned with a disc brake system, for example for a wheel of a vehicle.
A conventional disc brake system comprises a disc brake, and a hub which provides a mounting for a wheel. The hub is mounted, eg on a suspension link of a vehicle, for rotation about a central axis of the hub. The disc brake comprises a disc which is fixedly mounted on the hub for rotation therewith. The brake also comprises friction material pads arranged on opposite sides of the disc, and a piston and cylinder assembly operable to urge the pads into engagement with the disc, to brake the hub and hence the wheel. Conventionally, the piston and cylinder assembly is slidably mounted and a caliper bridging an edge of the disc is fixed to a cylinder of the assembly. One friction pad is acted on directly by the piston and cylinder assembly while the other pad is mounted on the caliper on the opposite side of the disc. Operation of the assembly presses one pad against the disc and causes sliding movement of the cylinder of the assembly and of the caliper to bring the other pad into engagement with the disc, thereby applying a braking force to the disc and hence to the hub. Such a disc brake generates considerable quantities of heat which limits the materials which can be used and, eg because of thermal expansion effects, can adversely affect the performance of the brake. In order to remove some of the heat generated, it is known to provide cooling passages through the disc through which air is drawn by centrifugal force (see eg WO 97/21042 and GB 2 001 716 A). However, this solution complicates the manufacture of the disc and is not available when the disc is thin (as is desirable to save weight).
In WO 98/25804, a disc brake system is described in which two discs are mounted on the same hub. The use of two discs reduces the heat generated at each disc but makes it even more desirable for the discs to be thin. As described in WO 98/25804, each disc is mounted on the hub by mounting means which is arranged so that the hub and the discs rotate about the central axis of the hub as a unit but the discs can perform axial sliding movement on the hub. The system also comprises a piston and cylinder assembly having its cylinder fixed relative to a suspension link of a vehicle, the cylinder being integrally formed with the link. The system also comprises a caliper fixed relative to the cylinder, the caliper providing supports for friction material pads of the system, including pads between the two discs. The pad furthest from the assembly is fixed to the caliper but the remaining pads are slidably mounted thereon. When the piston and cylinder assembly is operated, a pad operated upon by the assembly and the pads between the discs slide on the caliper, and the discs slide on the hub until each disc is engaged on both sides by a pad.
In WO 98/25804, the hub has a mounting portion which is generally in the shape of a hollow cylinder, and the mounting means mounts the discs on the external surface of the mounting portion. The mounting means described comprises a plurality of axially-extending grooves formed in the hub and teeth projecting from the discs into the grooves, each tooth being a sliding fit in one of said grooves.
It is an object of the present invention to provide improved cooling for a disc of a disc brake system in which the disc can perform axial sliding movement on a hub.
The invention provides a disc brake system comprising a disc, and a hub which is arranged to rotate about an axis thereof, the hub comprising a mounting portion which is generally in the shape of a hollow cylinder, the system also comprising mounting means by which the disc is mounted on the external surface of said mounting portion for rotation with said hub as a unit about said axis and so that the disc can perform axial sliding movement on said hub, characterised in that said hub carries vanes arranged so that, during rotation of the hub about said axis, the vanes act to force air into the interior of said mounting portion, and in that said mounting portion has openings therethrough arranged so that air forced into the interior of the mounting portion passes through said openings and flows over said disc.
In a disc brake system according to the invention, the disc is cooled by the air in a simple manner which allows thin discs to be used. The present invention is applicable to a disc brake system of the type described in WO 98/25804 but is also applicable to other disc brake systems having a disc which is axially movable on a hub.
In a disc brake system according to the invention, said mounting means may comprise a plurality of axially-extending grooves formed in the hub and teeth projecting from the disc into the grooves, each tooth being a sliding fit in one of said grooves, said openings being formed in portions of the hub which are between the grooves. The grooves may be in groups as disclosed in WO 98/25804. Other forms of mounting means are also possible, for example the roller arrangement disclosed in WO 98/26192.
Where the hub has grooves as afore-mentioned, a system according to the invention may also comprise a plurality of leaf springs mounted on said hub on portions thereof which are between said grooves, the leaf springs acting to apply radial force between the disc and the hub (such leaf springs are disclosed in WO 98/25804 and act to control the movement of the disc on the hub). In this case, said springs may have openings therethrough which correspond to said openings in the hub, thereby allowing passage for the air.
Conveniently, said vanes are mounted on a phonic wheel of an anti-lock braking system mounted on said hub.
In order to accommodate the movement of the disc on the hub, said openings in the hub may be in the form of slits which are elongated in the axial direction.
There now follows a detailed description, to be read with reference to the accompanying drawings, of two disc brake systems which are illustrative of the invention.